Using the immense power of Sandia National Nuclear Lab's Z machine researchers …

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Water, while one of the most abundant compounds on the planet and one of the most crucial compounds to life on earth, is one of the oddest. It exhibits physical characteristics that are completely anomalous from other molecules with similar size and structure. This page lists 63 anomalies that water exhibits, ranging from the well-known fact that at one atmosphere it expands upon freezing to the relatively unknown fact that water's viscosity decreases with pressure below 33°C. What many may not know is that water has more than the three phases that are typically associated with it—ice at low temperature, liquid water at moderate temperatures, and steam at high temperatures. In reality water (H2O) has 14 different phases, solid water (ice) contributing 12 different phases alone.

Since water behaves so strangely and is of such critical importance to life on Earth,scientists have long sought to fully understand all of its properties. One area of research is looking into understanding what happens to water at extreme conditions. It is believed that the accepted phase diagram of water at extreme temperatures and pressures may not be correct. For everyday life this doesn't matter. However, when you want to initiate a nuclear fusion reaction or understand the phase of ice that may be found on a celestial body, one needs a very accurate description of the water or ice at those conditions.

There are few places on earth capable of reproducing conditions as extreme as those described above. One place that can is the Sandia National Nuclear Laboratory, home of the Z machine. The Z machine is the largest X-ray generator in the world and can be used to create extreme temperatures and pressures with the goal (among others) of gathering data for the simulation of nuclear weapons. Understanding how water exists at the conditions generated in the Z machine is important; during its current operation the Z machine sends a 20-million ampere pulse of electricity through water which gets compressed to incredibly high pressures. Normally this water acts as an insulator and switch, but a series of planned upgrades to further strengthen the Z machine could mean different behavior from the water at such extreme conditions.

By passing the 20 million amperes of current through a small aluminum chamber, a magnetic field is created that isentropically compresses aluminum plates that sandwich a thin (25 micron) layer of water to pressures ranging from 50,000 to 120,000 atmospheres. For reference, what you experience at sea level is one atmosphere of pressure. What the researchers found was at these incredibly high pressures, water was squeezed into ice—ice VII to be exact, which was subsequently hotter than the boiling point of water at atmospheric pressure. As described by Sandia researcher Daniel Dolan, "Apparently it's virtually impossible to keep water from freezing at pressures beyond 70,000 atmospheres." Maybe that's a bit of an understatement, but it is very important to know for future operation of the Z machine and similar devices. The physical properties of ice—any ice phase—are vastly different from their liquid counter part.

As an aside, I have always enjoyed reading about and seeing videos of people who attempt to see who can light their grill the fastest, and have always loved the video of the guy who dumped a dewar of LOX on his grill bringing it to temperature in less than a second, vaporizing most of his grill in the process. What does this have to do with hot ice and the Z machine, you ask? Well, it turns out that at these pressures and temperatures the water underwent a phase transition from liquid to solid in less than 100 nanoseconds. Sadly since the ice here is so hot, it won't let you cool your beer any faster.

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Matt Ford
Matt is a contributing writer at Ars Technica, focusing on physics, astronomy, chemistry, mathematics, and engineering. When he's not writing, he works on realtime models of large-scale engineering systems. Emailzeotherm@gmail.com//Twitter@zeotherm